JPH06107943A - Thermoplastic polyurethane composition - Google Patents

Abstract

PURPOSE:To obtain a thermoplastic polyurethane resin composition, capable of producing flexible injection moldings having a high dimensional accuracy even when a long injection molding time is not adopted and having a low hardness. CONSTITUTION:The objective thermoplastic polyurethane composition is composed of (a) a thermoplastic polyurethane, containing a polymer diol component having >=1700 number-average molecular weight as a soft segment and having <=4.0wt.% nitrogen atom content (Na) and (b) a thermoplastic polyurethane having >=3.5wt.% nitrogen atom content (Nb) and <=0.85dl/g inherent viscosity. This thermoplastic polyurethane composition has (1) >=0.5wt.% difference (Nb-Na), (2) 0-80 deg.C difference (Tfb-Tfa) between the flow starting temperature (Tfb) of the component (b) and the flow starting temperature (Tfa) of the component (a) and (3) (60/40) to (98/2) weight ratio of the components [(a)/(b)].

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to thermoplastic polyurethane compositions. INDUSTRIAL APPLICABILITY Since the thermoplastic polyurethane composition of the present invention has a low hardness and gives a molded product with high dimensional accuracy by injection molding, it is useful as a material for molded products that require flexibility and dimensional accuracy.

[0002]

2. Description of the Related Art Thermoplastic polyurethane resins are impact resistant,
Since it has excellent properties such as bending resistance, abrasion resistance, low temperature characteristics, and oil resistance, it is widely used as a molding material. Moreover, in recent years, its soft texture and moist touch have attracted attention, and its application is expanding further as a flexible injection-molded product such as a watch band, a shoe sole, a camera grip, and parts for electric / precision machinery. However,
Thermoplastic polyurethanes generally have low dimensional accuracy of injection-molded products, and have the drawback that a long mold cooling time is required to achieve sufficient dimensional accuracy. In reality, almost no thermoplastic polyurethane of 85 or less gives an injection-molded product having a dimensional accuracy as high as practicable as a part for the above-mentioned electric / precision machinery.

[0003]

DISCLOSURE OF THE INVENTION The inventors of the present invention have developed a low hardness thermoplastic polyurethane resin capable of producing a flexible injection molded product having high dimensional accuracy even when a long injection molding time is not adopted. In order to minimize the increase in overall hardness and to significantly improve the dimensional accuracy in injection molding, by mixing a small amount of high-hardness thermoplastic polyurethane with low-hardness thermoplastic polyurethane. In the composition consisting of this low-hardness thermoplastic polyurethane and the high-hardness thermoplastic polyurethane, the mutual outflow starting temperature may be increased so that unmelting of the high-hardness thermoplastic polyurethane does not occur during injection molding. We found that the combination of thermoplastic polyurethanes that reduces the difference in
The present invention has been completed.

[0004]

Means for Solving the Problems That is, according to the present invention, the nitrogen atom content rate (Na) in which a polymer diol component having a number average molecular weight of 1700 or more is used as a soft segment is 4.0 wt%.
The following thermoplastic polyurethane (a) and the nitrogen atom content (Nb) is 3.5% by weight or more and the inherent viscosity is 0.8.
The thermoplastic polyurethane (b) is 5 dl / g or less, the difference between Nb and Na (Nb-Na) is 0.5% by weight or more, and the outflow starting temperature (Tfb) of the thermoplastic polyurethane (b) is The difference (Tfb-Tfa) in the outflow starting temperature (Tfa) of the thermoplastic polyurethane (a) is 0 to 80 ° C.
And the weight ratio of the thermoplastic polyurethane (a) to the thermoplastic polyurethane (b) is (a) / (b).
Is within the range of 60/40 to 98/2.

The thermoplastic polyurethane (a) and the thermoplastic polyurethane (b) constituting the thermoplastic polyurethane composition of the present invention are each generally a polymeric diol,
It is produced by subjecting a diisocyanate and a chain extender to a urethane reaction, and the molecular main chain is substantially composed of a soft segment composed of a polymer diol component and a hard segment composed of a diisocyanate component and a chain extender component.

The number average molecular weight of the polymer diol component constituting the thermoplastic polyurethane (a) must be 1700 or more. If the number average molecular weight is less than 1700, the dimensional accuracy and mechanical performance of the obtained injection molded product will be insufficient. The upper limit of the number average molecular weight of the polymer diol component of the thermoplastic polyurethane (a) is not particularly limited, but if it is too high, the fluidity of the resin may decrease and injection molding may become difficult. In terms of easiness, dimensional accuracy of the obtained injection-molded article and high mechanical performance, the number average molecular weight is 2000 to 5000.
It is preferably within the range. On the other hand, the number average molecular weight of the polymer diol component of the thermoplastic polyurethane (b) is
It is not particularly limited, but if it is too high, the fluidity of the resin may decrease, making injection molding difficult, and if it is too low, the mechanical performance of the obtained injection molded product may be insufficient. Therefore, it is preferably in the range of 500 to 5000. In addition, in the thermoplastic polyurethane (a) and the thermoplastic polyurethane (b), the number average molecular weight of the polymer diol component contained therein is substantially the same as the number average molecular weight of the polymer diol used as a raw material for production. As the polymer diol component, poly (tetramethylene adipate) diol, poly (3-methylpentamethylene adipate) diol, poly (hexamethylene adipate) diol, 1,9-nonanediol and 2-
Poly (alkylene adipate) diol containing a mixture with methyl-1,8-octane diol as an alkylene glycol component, 1,9-nonane diol and 2-methyl-
Polyester diols such as poly (alkylene adipate) diol and polycaprolactone diol containing a mixture of 1,8-octanediol and 1,4-butanediol as an alkylene glycol component; poly (hexamethylene carbonate) diol, 1,9-nonane Diol and 2
-Polycarbonate diol such as poly (alkylene carbonate) diol containing a mixture with methyl-1,8-octane diol as alkylene glycol component; polymeric diol such as polyether diol such as polyethylene glycol, polypropylene glycol, polyoxytetramethylene glycol The structural unit derived from is illustrated. The polymer diol component in the thermoplastic polyurethane (a) and the polymer diol component in the thermoplastic polyurethane (b) may have the same or different chemical structure and molecular weight.

4,4'-Diphenylmethane diisocyanate is obtained as the diisocyanate and 1,4-butanediol is obtained as the chain extender for producing the thermoplastic polyurethane (a) and the thermoplastic polyurethane (b), respectively. It is preferable because the dimensional accuracy of the injection molded product is likely to be further improved.

The nitrogen atom content (Na) expressed in weight% of the thermoplastic polyurethane (a) must be 4.0 weight% or less. A thermoplastic polyurethane having a Na content of more than 4.0% by weight has a too high hardness, so that a thermoplastic polyurethane composition having a low hardness cannot be obtained. Nitrogen atom content (Nb) in% by weight of thermoplastic polyurethane (b)
Must be 3.5% by weight or more. When Nb is less than 3.5% by weight, the effect of improving the dimensional accuracy of the obtained injection-molded product is not sufficiently exhibited, and a long injection molding time is required to improve the dimensional accuracy. Further, the difference between Nb and Na (Nb-Na) needs to be 0.5% by weight or more. When the difference is less than 0.5% by weight, the effect of improving the dimensional accuracy of the injection-molded article derived from the blending of the thermoplastic polyurethane (b) is not sufficiently exhibited. The nitrogen atom content of the thermoplastic polyurethane depends on the molecular weight of the manufacturing raw materials (polymer diol, diisocyanate and chain extender),
It can be arbitrarily adjusted by selecting the composition ratio and the like.

The inherent viscosity (ηinh) of the thermoplastic polyurethane (b) is required to be 0.85 dl / g or less. When the logarithmic viscosity number is larger than 0.85 dl / g, the effect of improving the dimensional accuracy of the injection molded product is not sufficiently exhibited, and a long injection molding time is required to improve the dimensional accuracy. The lower limit of the logarithmic viscosity number of the thermoplastic polyurethane (b) is not particularly limited, but if it is too low, the difference in melt fluidity with the thermoplastic polyurethane (a) becomes large, and the quality of the obtained molded product tends to be nonuniform. Therefore, it is desirable that the logarithmic viscosity number does not fall below 0.4 dl / g. On the other hand, the logarithmic viscosity number of the thermoplastic polyurethane (a) is not particularly limited, but if it is too high, the melt fluidity is poor and the injection moldability is lowered, and if it is too low, the mechanical performance of the obtained molded article is reduced. Therefore, the logarithmic viscosity number is preferably within the range of 0.7 to 1.3 dl / g.

Difference in outflow starting temperature (Tfb-T) between the thermoplastic polyurethane (a) and the thermoplastic polyurethane (b)
fa) needs to be in the range of 0 to 80 ° C. If Tfb-Tfa exceeds 80 ° C., the thermoplastic polyurethane (b) will have poor fluidity during injection molding, and the resulting injection molded article will be inhomogeneous.

The method for producing the above-mentioned thermoplastic polyurethane (a) and thermoplastic polyurethane (b) used in the present invention is not particularly limited, and a known polyurethane production method can be adopted. As a preferred production method, the polymer polyol, diisocyanate such as 4,4′-diphenylmethane diisocyanate, and chain extender such as 1,4-butanediol are continuously added using a multi-screw extruder in the absence of a solvent. A method of reacting with a melt polymerization method can be mentioned. Further, the thermoplastic polyurethane (a) and the thermoplastic polyurethane (b) respectively contain a heat stabilizer, an antioxidant, a light stabilizer, a flame retardant,
Lubricants, colorants and the like may be optionally added.

In the thermoplastic polyurethane composition of the present invention, the weight ratio of the thermoplastic polyurethane (a) to the thermoplastic polyurethane (b) is (a) / (b) 60 / 40-9.
It is necessary to be within the range of 8/2. When the amount of the thermoplastic polyurethane (b) is more than 40 parts by weight with respect to 60 parts by weight of the thermoplastic polyurethane (a), the hardness of the thermoplastic polyurethane composition becomes high, and the flexibility of the obtained injection-molded product becomes insufficient. Will be enough. Further, when the amount of the thermoplastic polyurethane (b) is less than 2 parts by weight relative to 98 parts by weight of the thermoplastic polyurethane (a), the effect of improving the dimensional accuracy of the obtained injection-molded product is not sufficiently exhibited, and the dimensional accuracy A long injection molding time is required to increase the temperature. The form of the thermoplastic polyurethane composition of the present invention is not particularly limited, and a blend of thermoplastic polyurethane (a) chips or flakes and thermoplastic polyurethane (b) chips or flakes, thermoplastic polyurethane (a). An example is a uniform blend obtained by melt-kneading and the thermoplastic polyurethane (b).

The thermoplastic polyurethane composition of the present invention comprises
Various molded articles can be manufactured according to an injection molding method such as that adopted for ordinary thermoplastic polyurethane. INDUSTRIAL APPLICABILITY The thermoplastic polyurethane composition of the present invention is particularly useful as a material for injection-molded articles that require both flexibility and dimensional accuracy, such as parts for electric and precision machines.

[0014]

In the thermoplastic polyurethane composition of the present invention, the auxiliary component thermoplastic polyurethane (b) does not significantly impair the low hardness derived from the main component thermoplastic polyurethane (a) during injection molding. Since it acts as a nucleating agent, it is presumed that the dimensional accuracy of the obtained injection molded product can be improved.

[0015]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the examples, compound names are represented by the abbreviations shown in Table 1 below.

[0016]

[Table 1]

The number average molecular weights of the thermoplastic polyurethanes obtained in Examples and Comparative Examples were determined based on their acid value and hydroxyl value. The nitrogen atom content (Na and Nb) of the thermoplastic polyurethane was quantified by elemental analysis. The logarithmic viscosity number (ηinh) of thermoplastic polyurethane is
It measured using the Ostwald viscosity tube (solvent: dimethylformamide; concentration: 0.5%; measurement temperature: 30 ° C.).
Regarding the outflow start temperature (Tfa and Tfb) of the thermoplastic polyurethane, the polymer outflow rate was measured at intervals of 3 ° C. by a temperature raising method using a Koka type flow tester (nozzle: hole diameter 1 mm, hole length 10 mm; load: 100 kg
f; temperature rising rate: 5 ° C./min), polymer outflow rate is 1 × 1
The temperature was plotted against the temperature in the range of 0 ^{−3 to} 5 × 10 ⁻³ ml / sec, the temperature at which the outflow rate was 0 ml / sec was determined by extrapolation, and this was taken as the outflow start temperature. The dimensional accuracy of injection-molded articles of the thermoplastic polyurethane compositions obtained in Examples and Comparative Examples was evaluated by the following method. That is, an injection molding machine (made by NISSEI PLASTIC,
5.0 ounces) and a diameter of 12 with a peripheral gate
Using a disk mold of 0 mm and thickness of 2 mm (mold temperature: 30 ° C.), a disc-shaped test piece with a diameter of about 120 mm and a thickness of 2 mm was produced under the conditions of an injection time of 15 seconds and a cooling time of 50 seconds. Then, using this test piece, the molding strain (%) was calculated based on the following mathematical formula, which was used as the evaluation standard of the dimensional accuracy of the injection molded product. The closer the molding strain value is to 0%, the higher the dimensional accuracy is.

[0018]

[Equation 1]

[Here, L represents the distance (mm) from the die gate portion on the outer circumference of the disk in the test piece to the outer circumference on the opposite side through the center of the disk]

The hardness of the thermoplastic polyurethane compositions obtained in the examples and comparative examples is JIS-K-731.
According to 1, the hardness was measured using an A hardness meter.

Example 1 PMP having a number average molecular weight of 4000 as a polymeric diol
A, BD, and MDI are liquid from a storage tank heated to 85 ° C, 50 ° C, and 50 ° C, respectively, and polymer diol /
An MDI / BD molar ratio of 1/3/2 was continuously charged into the same-direction twin-screw extruder by a metering pump to carry out continuous melt polymerization. At this time, the heating zone of the extruder was divided into three zones of a front portion, an intermediate portion and a rear portion, and the temperature of the intermediate portion was 230 ° C and the temperature of the rear portion was 200 ° C. The produced polymer was continuously extruded in water in the form of a strand, pelletized, and then vacuum dried at 80 ° C. for 6 hours. The thus obtained thermoplastic polyurethane [corresponding to the thermoplastic polyurethane (a)] has a nitrogen atom content of 1.7% by weight, ηinh of 0.95 dl / g, and an outflow starting temperature ( Tfa) was 151 ° C. The molar ratio of polymer diol / MDI / BD is 1/8.
A thermoplastic polyurethane [corresponding to thermoplastic polyurethane (b)] was obtained in the same manner as described above except that the ratio was changed to 5 / 7.5. The nitrogen atom content of this thermoplastic polyurethane was 3.9% by weight, and ηinh was 0.1.
77 dl / g, and the outflow starting temperature (Tfb) is 2
It was 02 ° C. The dry pellets of the thermoplastic polyurethane (a) and the thermoplastic polyurethane (b) were mixed with (a)
A disk-shaped test piece was obtained by blending so that the weight ratio of / (b) was 80/20, and then melt-kneading and injection-molding by the above-mentioned injection molding method. Table 2 shows the obtained evaluation results.

Examples 2 to 5 and Comparative Examples 1 to 6 Two types of thermoplastic polyurethanes shown in Table 2 (both of which are shown in Table 2)
(Polymer diol, MDI and BD obtained by melt-polymerizing) are blended in a predetermined weight ratio, and melt kneading / injection molding is performed by the above-mentioned injection molding method.
A disc-shaped test piece was obtained (in Comparative Example 2, 1
Only the seed thermoplastic polyurethane was subjected to injection molding).
Table 2 shows the obtained evaluation results.

[0023]

[Table 2]

In Table 2, "Faulty flow" in the column of "Dimensional accuracy of molded article" in Comparative Example 5 means that the fluidity of the resin at the time of injection molding is poor and the molded article having a predetermined shape (disk shape). It means that the test piece) was not obtained.

From Table 2 above, in the compositions of the present invention of Examples 1 to 5, since the hardness is less than 80 and the molding strain is 2% or less, injection molded products having excellent flexibility and high dimensional accuracy are obtained. It can be seen that it was obtained. On the other hand, when ηinh of the thermoplastic polyurethane (b) is larger than 0.85 dl / g (Comparative Example 1), when the thermoplastic polyurethane (b) is not used at all (Comparative Example 2), the thermoplastic polyurethane (b) is used.
In the case where the nitrogen atom content is less than 3.5% by weight (Comparative Example 3) and the number average molecular weight of the polymer diol component of the thermoplastic polyurethane (a) is less than 2000 (Comparative Example 6), both are obtained. It can be seen that the injection-molded product obtained has low dimensional accuracy. When the thermoplastic polyurethane (b) is more than 40 parts by weight with respect to 60 parts by weight of the thermoplastic polyurethane (a) (Comparative Example 4), the hardness of the thermoplastic polyurethane composition is high and the obtained injection-molded article is obtained. It turns out that the flexibility of is insufficient. Further, when the difference in the outflow starting temperature (Tfb-Tfa) between the two types of thermoplastic polyurethane exceeds 80 ° C. (Comparative Example 5), the fluidity at the time of injection molding is poor and molding of a satisfactory shape is performed. You can see that the product was not obtained.

[0026]

According to the present invention, as is apparent from the above-mentioned embodiments, a thermoplastic resin having a low hardness capable of producing an injection-molded article having high dimensional accuracy even when a long injection-molding time is not adopted. A polyurethane composition is provided. INDUSTRIAL APPLICABILITY The thermoplastic polyurethane composition of the present invention is useful as a material for producing an injection-molded article having excellent flexibility and high dimensional accuracy.

Claims (1)

[Claims] 1. A nitrogen atom content rate (N in which a polymer diol component having a number average molecular weight of 1700 or more is used as a soft segment)
Thermoplastic polyurethane (a) containing 4.0% by weight or less of a)
And a thermoplastic polyurethane (b) having a nitrogen atom content (Nb) of 3.5% by weight or more and a logarithmic viscosity number of 0.85 dl / g or less, and a difference between Nb and Na (Nb-Na).
Is 0.5% by weight or more, and the difference (Tfb-T) between the outflow starting temperature (Tfb) of the thermoplastic polyurethane (b) and the outflow starting temperature (Tfa) of the thermoplastic polyurethane (a).
fa) is in the range of 0 to 80 ° C., and the weight ratio of the thermoplastic polyurethane (a) to the thermoplastic polyurethane (b) is (a) / (b) in the range of 60/40 to 98/2. And a thermoplastic polyurethane composition.